de la Cruz R R, Pastor A M, Delgado-García J M
Departamento de Fisiología y Biología Animal, Facultad de Biología, Sevilla, Spain.
Eur J Neurosci. 1993 Mar 1;5(3):232-9. doi: 10.1111/j.1460-9568.1993.tb00489.x.
The electrical activity of antidromically identified abducens internuclear neurons selectively deprived of their target motoneurons was recorded in chronic alert cats. Target motoneurons were killed by the injection of the cytotoxic lectin of Ricinus communis into the medial rectus muscle. Following target removal, the discharge pattern of abducens internuclear neurons showed an overall decrease in firing rate, a significant reduction in their sensitivity to eye position and velocity, and the presence of anomalous responses such as bursts of spikes associated with off-directed saccades. The decreased excitability of abducens internuclear neurons correlated well with a marked reduction in the synaptic efficacy of their inputs. Thus, both excitatory and inhibitory synaptic potentials of vestibular origin showed a noticeable decrease in amplitude. The alterations in firing properties and synaptic transmission were only observed during an initial period of 3 weeks following ricin injection. Within 1 month the electrophysiological parameters returned to control values and remained unaltered for 1 year. Retrograde labelling of abducens internuclear neurons revealed that no cell death occurred after target loss. The anterograde axonal labelling of these neurons showed a progressive decrease in the density of their axonal terminals, and no sign of redistribution to other areas was found. These findings indicate that abducens internuclear neurons are not dependent on the presence of their natural target cells, either for the survival or for the maintenance of appropriate physiological signals.
在慢性清醒猫中记录了逆向识别的展神经核间神经元的电活动，这些神经元被选择性地剥夺了其靶运动神经元。通过将蓖麻毒蛋白的细胞毒性凝集素注射到内直肌中来杀死靶运动神经元。去除靶神经元后，展神经核间神经元的放电模式显示出放电频率总体下降，对眼位和速度的敏感性显著降低，并且出现了异常反应，如与向外扫视相关的一串动作电位。展神经核间神经元兴奋性的降低与其输入突触效能的显著降低密切相关。因此，前庭起源的兴奋性和抑制性突触电位的幅度均明显下降。放电特性和突触传递的改变仅在注射蓖麻毒素后的最初3周内观察到。1个月内，电生理参数恢复到对照值，并在1年内保持不变。展神经核间神经元的逆行标记显示，靶神经元丧失后没有细胞死亡发生。这些神经元的顺行轴突标记显示其轴突终末密度逐渐降低，未发现重新分布到其他区域的迹象。这些发现表明，展神经核间神经元无论是在存活还是在维持适当生理信号方面，都不依赖于其天然靶细胞的存在。
